This project is currently focuses on the hormonal, neural, and pharmacological factors underlying vocal expression in nonhuman primates. Major findings this year include: 1. in situ hybridization techniques found evidence for RNA specific to the synthesis of vasopressin and oxytocin in parts of the marmoset hypothalamus, confirming our earlier finding on these neuropeptides using immuno-cytochemistry. 2. The separation response of infant rhesus macaques was shown to be a dynamic process with respect to vocal behavior, in that the calling rate of one vocal sub-type decreased over time, while the calling rate of a different subtype increased over the same time period.